Our invention relates to a compatible data storage apparatus capable of selective use with interchangeable record disk assemblies of two or more different storage capacities at as many different data transfer speeds. We envisage flexible magnetic disk cartridges as a typical form of disk assemblies for use with the data storage apparatus of our invention, although we do not wish our invention to be limited to this particular application.
Three and a half inch flexible magnetic disks are commercially available today with storage capacities of one, two, and four megabyte. All these disks of the different capacities are offered in cartridge form, with plastic housings of the same shape and size (FIGS. 1-3). The two and four megabyte disk cartridges, however, have markings in the form of small, square openings or windows formed in different predetermined positions in their housings. These windows are intended to enable the associated compatible disk drive to discriminate between the two and four megabyte disk cartridges. We will therefore refer to the windows as the capacity discriminate windows hereinafter in this specification. The one megabyte disk cartridge has no capacity discriminate window and so is distinguished from the two and four megabyte disk cartridges.
In a compatible disk drive for use with at least the two and four megabyte disk cartridges, two disk sensors have customarily been employed for discriminating between the two different types of disk cartridges by detecting the capacity discriminate windows in their housings. It has also been customary for the compatible disk drive to incorporate two additional sensors. One of these has been used for finding whether the write protect window in each disk cartridge is open or closed, and the other for detecting the loading of either type of disk cartridge in the disk drive. The detection of the loading of a disk cartridge in the disk drive is essential for the production of the disk change signal and "ready" signal which are both standard in the disk drive art.
Thus, conventionally, at least four sensors have been used in the compatible disk drive of the type under consideration. Being constituted of Microswitches (trade name) or optical devices, such sensors have made the disk drive complex and expensive in construction, difficult of assemblage, unreliable in operation.